Glioblastoma is a primary cancer of the central nervous system. Unfortunately, current treatments are unable to control the invasiveness of the tumor, leading to a 95% recurrence rate. Moreover, although radiation therapy has produced the largest improvement in survival for these patients, it is also associated with increased tumor invasiveness, perhaps contributing to the high recurrence rate. Our preliminary work suggests that CD147, a protein which is commonly overexpressed in glioblastoma, may contribute to this invasion, in particular the increased invasion after radiation exposure. Interestingly, CD147 works to promote invasion in cancer cells via intercellular communication: carcinomas secrete CD147 to induce neighboring fibroblasts to produce matrix metalloproteinases (MMPs), which degrade the extracellular matrix. In glioblastoma, we have found that extracellular vesicles from glioblastoma cells not only contain CD147, but their CD147 levels are higher if the cells are irradiated. Similarly, we found that glioblastoma cells release extracellular vesicles that increase MMP production in astrocytes, and that MMP production is further increased if the extracellular vesicles are from irradiated glioblastoma cells. Together, these studies suggest that CD147 may play a key role in both the invasiveness of glioblastoma tumors and the increased invasion observed following irradiation. Therefore, this study proposes two specific aims to test the central hypothesis that glioblastoma cells use extracellular vesicles containing CD147 to mediate a pro-invasive environment. We further hypothesize that radiation increases the levels of CD147 in extracellular vesicles, resulting in increased invasiveness. In Aim 1, we will examine in vitro whether CD147 in the extracellular vesicles of glioblastoma cells can induce astrocytes and microglia to promote invasion through MMP production, and whether radiation enhances this process. Through knockdown of CD147, we will examine how CD147 controls drivers of invasion by analyzing the MMP protein and mRNA levels, the amount and activity of secreted MMPs, and the signaling pathways leading to MMP production. We will also test the effects of CD147 on functional endpoints using invasion and migration assays. In Aim 2, we will demonstrate in vivo that CD147 is an important mediator of tumor invasiveness, in particular after radiation exposure. We will use an orthotopic mouse model of glioma consisting of wild-type and CD147-knockdown tumor cells. Using a state-of-the-art system that mimics clinical therapy, we will perform specific CT-image guided X-ray irradiation of the tumors. We will examine differences in survival, number of metastases in the brain, and immunohistological endpoints. Radiation is expected to increase invasion in the CD147 wild-type tumors, relative to non-irradiated controls. However, we predict that the combination of radiation and CD147 knockdown will act synergistically to generate the lowest level of invasion among the groups. These results may suggest CD147 inhibitors as an important adjuvant to radiation therapy, contributing to reduced invasion and thus improved patient survival.